1. Field of the Invention
The present invention relates to a resin sealing apparatus for sealing an article to be sealed such as, for instance, a semiconductor device with resin.
2. Discussion of Background
FIGS. 12 and 13 are respectively a plane view and a side view showing a conventional resin sealing apparatus which specifically show a lower die for sealing a semiconductor device with resin. In FIGS. 12 and 13, a reference numeral 1 designates a base, a numeral 2 designates an ejector portion fixed onto the base 1, a numeral 3 designates a surface plate fixed onto the ejector portion 2, which includes a heater (not shown), a numeral 4 designates a chase block mounted on the surface plate 3, numerals 5 designate knock pins inserted in the chase block 4 and the surface plate 3, and numerals 6A designate bolts for fixing the chase block 4 to the surface plate 3. The chase block 4 is supported by the surface plate 3 which functions as a supporting member. The heads of the knock pins 5 and the bolts 6A respectively sink in the chase block 4 so as not to project from the upper surface of the chase block. Numerals 7 and 8 respectively designate cavities and runners formed in the chase block 4, numerals 9 designate end plates attached to a pair of opposing sides of the chase block 4 to close free ends of the runners 8, numerals 10 and 11A designate respectively guide pins in a cylindrical form which are fixed to the surface plate 3. An upper die (not shown) having a similar construction to the lower die is located facing the lower die. The upper die is provided with a position determining block 11B (which is indicated by an imaginary line) so as to be fitted to the position determining block 11A of the lower die. The fitting of the position determining blocks 11A and 11B is performed by convex and concave portions formed in the blocks. The upper die is also provided with guide pins which have fitting portions such as round holes or cylindrical projections so as to face the guide pins 10 mounted on the lower die so that the chase blocks of the upper and lower dies are assembled by fitting the position determining blocks 11A, 11B and the guide pins.
The function of the conventional resin sealing apparatus will be described.
Lead frames (not shown) each having a semiconductor device (not shown) and a wire bonded thereto are placed in the cavities 7 of the chase block 4 of the lower die. The upper and lower dies are assembled and fastened by means of a pressing machine (not shown) by fitting the fitting portions of the guide pins and the position determining blocks 11A, 11B of the upper and lower dies. Since the positions of the chase block 4 and the surface plate 3 are determined by means of the knock pins 5 in the upper and lower dies respectively, the positions of the chase blocks of the upper and lower dies are indirectly determined and they are assembled by determining the positions of the surface plates of the upper and lower dies by means of the round holes and the cylindrical projections of the guide pins and the position determined blocks 11A, 11B. Then, resin is injected into the cavities 7 through the runners 8. After the resin is cured in the cavities of the chase blocks of the upper and lower dies, which are heated at a predetermined temperature by heaters (not shown) installed in the surface plates, the upper and lower dies are separated, and resin-molded articles (not shown) cured in the cavities 7 are raised by the ejector portions. Then, the molded articles are removed from the upper and lower dies.
In the conventional resin sealing apparatus, since the positions of the chase blocks of the upper and lower dies are indirectly determined by supporting members such as the surface plates, there occurs an error in position between the chase blocks of the upper and lower dies due to an error of dimensions of the supporting members during machining and the difference of the thermal expansion of the upper and lower dies due to a change of temperature distribution of the parts of the dies. Such error in position results in faulty shape in the resin-molded articles.